The present invention relates to a sensor terminal and, more particularly, to a photoelectric smoke sensor terminal for converting an analog output signal from a photoelectric smoke sensor to a digital signal and for transmitting the digital signal to a main unit (receiver side) only when an address of the terminal is accessed by the main unit.
In a conventional terminal of this type, a photoelectric smoke sensor is coontinuously operated to supply an analog detected signal to an A/D converter. When an address of this terminal is accessed by a main unit, the converted digital signal is supplied from the A/D converter to the main unit. Therefore, a light-emitting element of the smoke sensor is normally ON, and light is constantly received by a light-receiving sensor and is transduced to an electrical signal, thus resulting in high power consumption.
In order to eliminate this drawback, a smoke sensor terminal having a pulse generator is proposed. A light-emitting element is intermittently turned on in response to an output from the pulse generator. The light from the light-emitting element is received by a light-receiving element. The light-receiving element converts light received to an electrical signal in accordance with the intensity thereof. This analog electrical signal is latched and converted to a digital signal, or is converted to a digital signal which is then latched. The latched digital signal is sent to the main unit when the main unit accesses this terminal. However, since the terminal of this type requires a pulse generator, a latch circuit and the like, the terminal configuration becomes complex and the terminal as a whole becomes expensive.